1. Field of the Invention
The present invention relates to a self-extinguishing room temperature vulcanizable polyorganosiloxane composition in which an elastomer is formed by cross-linking one or a mixture of silanol-terminated polydiorganosiloxanes containing phenyl groups bonded with the silicon atoms with an aminoxy group-containing organosilicon compound, characterized in that finely divided powder of aluminum hydroxide is incorporated therein for imparting a self-extinguishing property thereto.
2. Description of the Prior Art
There has been known a polyorganosiloxane composition which cures at room temperature to form an elastomer and a process for preparing the same, which comprises reacting a polydiorganosiloxane in which the molecular chain is terminated with hydroxyl groups, with an organosilicon compound in which a diorganoaminoxy group or cyclic organoaminoxy group is bonded with silicon atom to effect the cross-linkage, thereby liberating diorganohydroxylamine or cyclic organohydroxylamine. The composition is used frequently as a sealing material for construction purposes because of its property of forming an elastomer having an ultra-high elongation and a very low modulus. Recently, safety of buildings against fires has been demanded and flame-retarding properties are required of sealing materials. However, sealing materials comprising room temperature vulcanizable polyorganosiloxane compositions including the above described composition are generally not resistant to fire, but rather they have a continuous burning property. Thus, it has been difficult to satisfy the requirement for a flame-retarding property. There has been known a self-extinguishing, room temperature vulcanizable polyorganosiloxane composition characterized by containing platinum and finely divided powder of carbon as flame-retarding agent. However, this composition cannot form an elastomer of a low modulus and a high elongation, as is obtained from an aminoxy-group-containing organosilicon compound, because the cross-linking agent used therein is an oxime-group-containing silicon compound. In addition, since the elastomer thus obtained is black or dark in color due to the finely divided powder of carbon contained therein, the product is unsuitable for use as a sealing material for construction wherein a high elongation and a low modulus are indispensable and coloring in various colors is required.